The structure of tavorite LiFePO4(OH) from diffraction and GGA + U studies and its preliminary electrochemical characterization

Pure tavorite LiFePO 4 (OH) was synthesized through a hydrothermal route. A fine structural analysis was done by X-ray and neutron diffraction techniques. The structure consists of a three-dimensional network with iron( iii ) octahedra (FeO 6 ) sharing corners, forming chains that run along the b direction. These chains are interconnected by PO 4 tetrahedra, such as the resulting framework encloses tunnels of two different sizes running along the a and c axis. The lithium and hydrogen atoms were precisely localized in these tunnels. Theoretical (GGA + U ) calculations performed for LiFePO 4 X materials (X = OH, F) confirmed our results and revealed that a unique lithium position is expected in LiFePO 4 (OH), as experimentally observed. For the first time, lithium intercalation was shown to occur in LiFePO 4 (OH) through the reduction of Fe 3+ to Fe 2+ at an average voltage of ∼2.3 V ( vs. Li + /Li) with a good cyclability. A fine structural characterization of tavorite LiFePO 4 (OH) has revealed that Li and H occupy each a single position in this 3D framework. For the first time, Li intercalation was shown to occur in LiFePO 4 (OH), with a good cyclability.